Continued efforts are being made to solubilize and characterize the components of adenylate cyclase systems. Since Gpp(NH)p activates solubilized preparations of adenylate cyclase even though hormone response is lost, we have the means of at least testing whether the guanine nucleotide regulatory site resides on adenylate cyclase or on a separate component. Once purification of this component is achieved, we can then test whether the regulatory component contains distinct sites for binding and hydrolysis of GTP, the natural regulatory ligand. The purified components will then be used to reconstruct a system that interacts with hormone receptors and which may then become sensitive to the actions of hormones.